| 1 | import { useCallback, useEffect, useRef, useState } from "react"; |
| 2 | import { ArrowDown } from "lucide-react"; |
| 3 | |
| 4 | import { MessageBubble } from "@/components/MessageBubble"; |
| 5 | import { Button } from "@/components/ui/button"; |
| 6 | import { cn } from "@/lib/utils"; |
| 7 | import type { UIMessage } from "@/lib/types"; |
| 8 | |
| 9 | interface MessageListProps { |
| 10 | messages: UIMessage[]; |
| 11 | isStreaming: boolean; |
| 12 | } |
| 13 | |
| 14 | const NEAR_BOTTOM_PX = 48; |
| 15 | |
| 16 | /** |
| 17 | * Scrollable message log. Auto-sticks to the bottom as new content arrives, |
| 18 | * but only when the user was already at the bottom — preserving scroll |
| 19 | * position when they've scrolled up to read earlier turns. A floating |
| 20 | * "scroll to bottom" button appears whenever we're detached from the bottom. |
| 21 | */ |
| 22 | export function MessageList({ messages, isStreaming }: MessageListProps) { |
| 23 | const scrollRef = useRef<HTMLDivElement>(null); |
| 24 | const [atBottom, setAtBottom] = useState(true); |
| 25 | |
| 26 | const scrollToBottom = useCallback((smooth = false) => { |
| 27 | const el = scrollRef.current; |
| 28 | if (!el) return; |
| 29 | el.scrollTo({ |
| 30 | top: el.scrollHeight, |
| 31 | behavior: smooth ? "smooth" : "auto", |
| 32 | }); |
| 33 | }, []); |
| 34 | |
| 35 | // Keep the viewport pinned to the bottom as long as the user hasn't |
| 36 | // scrolled up. During streaming we do instant jumps (smooth scrolling each |
| 37 | // token fights the incoming animations); on settled updates we animate. |
| 38 | useEffect(() => { |
| 39 | if (!atBottom) return; |
| 40 | scrollToBottom(!isStreaming); |
| 41 | }, [messages, isStreaming, atBottom, scrollToBottom]); |
| 42 | |
| 43 | useEffect(() => { |
| 44 | const el = scrollRef.current; |
| 45 | if (!el) return; |
| 46 | const onScroll = () => { |
| 47 | const distance = el.scrollHeight - el.scrollTop - el.clientHeight; |
| 48 | setAtBottom(distance < NEAR_BOTTOM_PX); |
| 49 | }; |
| 50 | el.addEventListener("scroll", onScroll, { passive: true }); |
| 51 | return () => el.removeEventListener("scroll", onScroll); |
| 52 | }, []); |
| 53 | |
| 54 | if (messages.length === 0) { |
| 55 | return ( |
| 56 | <div className="flex h-full items-center justify-center text-sm text-muted-foreground"> |
| 57 | Say hi to get started. |
| 58 | </div> |
| 59 | ); |
| 60 | } |
| 61 | |
| 62 | return ( |
| 63 | <div className="relative flex min-h-0 flex-1 overflow-hidden"> |
| 64 | <div |
| 65 | ref={scrollRef} |
| 66 | className={cn( |
| 67 | "h-full overflow-y-auto scroll-smooth", |
| 68 | "[&::-webkit-scrollbar]:w-1.5", |
| 69 | "[&::-webkit-scrollbar-thumb]:rounded-full", |
| 70 | "[&::-webkit-scrollbar-thumb]:bg-muted-foreground/30", |
| 71 | "[&::-webkit-scrollbar-track]:bg-transparent", |
| 72 | )} |
| 73 | > |
| 74 | <div className="mx-auto flex w-full max-w-[64rem] flex-col gap-6 px-4 pt-4 pb-8"> |
| 75 | {messages.map((m) => ( |
| 76 | <MessageBubble key={m.id} message={m} /> |
| 77 | ))} |
| 78 | </div> |
| 79 | </div> |
| 80 | |
| 81 | {/* Top fade so messages slide under the header gracefully. */} |
| 82 | <div |
| 83 | aria-hidden |
| 84 | className="pointer-events-none absolute inset-x-0 top-0 h-6 bg-gradient-to-b from-background to-transparent" |
| 85 | /> |
| 86 | {/* Bottom fade so messages fade out behind the composer. */} |
| 87 | <div |
| 88 | aria-hidden |
| 89 | className="pointer-events-none absolute inset-x-0 bottom-0 h-8 bg-gradient-to-t from-background to-transparent" |
| 90 | /> |
| 91 | |
| 92 | {!atBottom && ( |
| 93 | <Button |
| 94 | variant="outline" |
| 95 | size="icon" |
| 96 | onClick={() => scrollToBottom(true)} |
| 97 | className={cn( |
| 98 | "absolute bottom-2 left-1/2 h-8 w-8 -translate-x-1/2 rounded-full shadow-md", |
| 99 | "bg-background/90 backdrop-blur", |
| 100 | "animate-in fade-in-0 zoom-in-95", |
| 101 | )} |
| 102 | aria-label="Scroll to bottom" |
| 103 | > |
| 104 | <ArrowDown className="h-4 w-4" /> |
| 105 | </Button> |
| 106 | )} |
| 107 | </div> |
| 108 | ); |
| 109 | } |
| 110 |